BIPARTITE PATELLA IN 35-YEAR-OLD FITNESS INSTRUCTOR: A CASE REPORT

Abstract

Background and Purpose

The patella plays an important role in knee biomechanics and provides anterior coverage of the knee joint. One to two percent of the population has an anatomical variant of patella called a bipartite patella that usually does not case pain. However, occasionally after injury or overuse during sport it can be a source of anterior knee pain. The purpose of this case report was to present a rare variant of bipartite patella and highlight conservative treatment of this condition.

Study Design

Case Report

Case Description

A 35-year-old female patient presented with persistent bilateral non-traumatic anterior knee pain of a six-year duration that was enhanced by strenuous kinds of sport activity. Standard radiographs and MRI revealed the presence of bipartite patella with medial pole cartilage edema bilaterally. Conservative care including physical therapy, extracorporeal shock wave therapy (ESWT), and viscosupplementation was utilized.

Outcome

After treatment VAS decreased to 0/10 from 5/10 in the left knee and 1/10 from 5/10 in the right knee. The Kujala Scores improved after treatment to 100 and 95 for the left and right knees respectively. The subject returned to full sport activity and work as a fitness instructor without pain and limitations.

Discussion

This case describes a rare finding of bilateral medial bipartite patella and the successful use of physical therapy with viscosupplementation in patellar pain caused by bipartite patella. It also supports the use of Extra Corporeal Shock Wave Therapy in bipartite patella pain as a supplement for therapy.

Level of Evidence

4

INTRODUCTION

The patella is the largest sesamoid bone in human body, positioned longitudinally in the quadriceps muscle fascia, between the quadriceps and patellar tendons. It plays an important role in knee biomechanics and provides anterior coverage of the knee joint. The prevalence of anterior knee pain in the female athletic and recreational athletic population reported in the literature is 12-13%.¹ Usually the patella begins to ossify at the age of three from a single ossification center. In some cases, however, there are two or more ossification centers that can form the patella. Overuse and repetitive trauma of this region may lead to excessive strain at the site of incomplete fusion causing pain and discomfort. The ossification centers generally fuse within the body of the patella in adolescence but sometimes this fusion is incomplete, resulting in a divided patella, known as a bipartite patella. Bipartite patella is considered a normal variant of the patella and is present in 1-2% of the population.² The majority of people having bipartite patella are unaware of the condition. Overgrowth of the supero- lateral quadrant of the patella is frequently observed but often is considered an incidental finding during differential diagnosis of knee injuries or disorders. Although the bipartite patella may be the only anatomical abnormality in painful knee, it may not be the source of pain. The exact frequency of painful bipartite patellae is unknown since only case reports or case series were available in the published literature.

Saupe² classified bipartite patella into three types according to anatomical variations depending on the localization of the unfused fragment of patella (Figure 1). In Type I, present in 5% of people with anatomical abnormalities of the patella,² the fragment is localized in the inferior pole. A more common variation present in 20% is Type II, where the fragment is localized at the lateral margin, while in 75% of the cases the bony fragment is localized at the supero-lateral portion of patella, and is described by Saupe as Type III.² This classification system does not describe a medial position of an unfused bony fragment of the patella. The authors found only one report of medial bipartite patella published 1978.² According to the literature regarding failed conservative treatment (when the pain is not relieved over several months) of bipartitie patella, surgical intervention should be considered. Several surgical methods for the treatment of the most common supero-lateral bipartite patella have been described. The most commonly used are: vastus lateralis release, lateral retinacular release technique or excision of the painful accessory fragment, and all these methods can be done either by open procedure or using arthroscopic technique.^3,4,5,6,7 Halpern and Hewitt achieved pain relief in a case of medial bipartite patella after excision of additional fragment.⁸

Figure 1.

Saupe`s classification of bipartite patella. Type I- inferior pole, Type II-lateral margin, Type III-superolateral margin.

Due to lack of sufficient description regarding this anatomic variation, the purpose of this case report was to present a rare variant of bipartite patella and highlight conservative treatment of this condition. The subject was informed that the data concerning the case would be submitted for publication.

SUBJECT PRESENTATION

A 35-year-old female a fitness instructor presented with persistent bilateral anterior knee pain for the previous six years without history of trauma. She reported an inability to perform strenuous kinds of sport activity like running and jumping. The pain also intensified during squats. There was a history of similar pain in the left knee at the age of 13. Diagnostic arthroscopy was performed at that time with all negative findings. Unfortunately, no radiographs were ordered at the time of surgery, and all diagnostic effort was focused on soft tissue structures like cartilage or meniscal lesions. After that arthroscopy she did not complain of knee pain for many years, until six years prior she began to experience pain a few times per year only after substantial effort. Over time the pain intensified and during the previous year the subject experienced pain during walking, climbing stairs, and at rest. After extensive activities performed for her work such as squats, jumping, and cycling, the subject would complain of swelling of both knees and the sensation of crepitus beneath both patellae. The subject was treated non-operatively for five years in another center mainly by nonsteroidal anti-inflamatory drugs (NSAID's) and glucosamine and chondroitin sulfate supplementation. Some physical therapy had been attempted, but the pain relief was partial and pain quickly returned.

EXAMINATION

Physical examination revealed tenderness over the supero-medial patellar pole on both knees. Based on negative tests including the Lachman, pivot shift, anterior and posterior drawer, Appley, McMurray, and varus/valgus stress tests meniscal and ligaments injuries were ruled out. A visible deformity and thickening over the supero- medial patellar pole was present the bilaterally. This was the most painful area of the knee. The subject scored 67 (on both the right and left knees) on the Kujala Scoring Questionnaire⁹ for patient reported outcomes related to patellofemoral dysfunction. (Table 1) This scoring system is designed to evaluate subjective symptoms and functional limitations in patients with patellofemoral pain and dysfunction. Minimum score is 0 and maximum is 100, the higher the score the better the function of the knee. ⁹

Table 1.

Kujala Score at the beginning of treatment for both knees

Parameter	Right	Left	Maximum Score possible
Limp while walking	5	5	5
Support	5	5	5
Walking	3	3	5
Using stairs	8	8	10
Squatting	4	4	5
Running	8	8	10
Jumping	2	2	10
Prolonged sitting	8	8	10
Knee pain	6	6	10
Knee swelling	6	6	10
Subluxations	6	6	10
Tight muscle atrophy	3	3	5
Flexion deficiency	3	3	5
Total Score	67	67	100

Standard radiographic examination (Anterior-posterior and skyline views) revealed a bipartite patella at the supero-medial pole of the patella in both knees (Figure 2). The accessory fragments were both irregular in shape. A larger fragment (2 cm width) was found in left knee compared with 1 cm width fragment present in the right knee. The Insal-Salvati index, the ratio of the patella tendon length (TL) to the length of the patella (PL), was 1,1 for the right knee and 1,0 for the left.

Figure 2.

Radiographs of the Mortise view (flexed skyline view) of both knees showing bilateral medial bipartite patellae

Further imaging techniques were scheduled to assess soft tissue structures,especially the articular cartilage and retinacula around the knee joints. Bilateral MRI examination confirmed the presence and the sizes of the accessory patellar bony fragments (Figure 3). The gaps between bony fragments and the bodies of the patella were filled by dense fibrous, heterogeneous tissue. Of note, the medial retinaculae were thickened at the both accessory fragment attachments. The hyaline cartilage beneath the medial poles of the patellae appeared heterogeneous with increased width, however, with continuity intact. The cartilage in the remaining parts of the patellar surfaces of the patellofemoral joints was thinned with notable fissuring and cracking, and subchondral bone edema noted. No other abnormalities of soft tissue structures around the patellae and knee were reported.

Figure 3.

Magnetic resonance imaging of the left knee. T1 axial sequence, note the medial side where an accessory fragment is visible. The interposed soft tissue is not homogeneous. Thickening of medial retinacula at the attachment and subchondral edema of the patella is also observed. Joint effusion is present.

INTERVENTIONS

The treatment plan was comprised of rest, limitation of sports activities, and also ultrasound therapy, accompanied by cryotherapy. Physical therapy interventions included stretching and strengthening exercises for hamstring and quadriceps muscles started immediately to ensure optimal length and strength of those muscles, supplemented by massage and soft tissue therapy for the quads, hamstrings and ilio-tibial bands, along with mobilization of the patella. The purpose was to regain full range of motion with proper patella tracking. Low intensity ultrasound and cryotherapy were utilized in the region of the additional patellar fragment and gap in order to reduce swelling and pain.

The patient was instructed in exercises for the gluteal, abductor and quadriceps muscles as well as stretching and deep tissue massage of gluteal, quadriceps, hamstring muscles and iliotibial band using a foam roller. At week four functional training, CORE stability interventions, and correction of faulty movement patterns during exercise were added. (Table 2) After eight weeks of rehabilitation and only partial improvement surgical excision of the accessory fragment was advised by the physician. The patient refused operative intervention.

Table 2.

Rehabilitation protocol

Week of rehabilitation	Rehab programe	Exercise/Physiotherapy	Purpose	Repetition
1-12	Hip strenghtening	Hip Abduction	Decreasing level of pain and swelling.	3x8
		Hip Adduction		3x8
		Hip Extension		3x8
		Hip IR/ER		3x8
		Unilateral supine bridge		3x8
		Side bridge (60 sec. or till maintaining proper position)		3x8
1-12	Flexibility	Individual practice with rehabilitant, mobilization, hip rotators, quadriceps and hamstring stretching	Regaining full non painful range of motion in the knee	10-30 min/day Hamstring held for 30-60 sec with 30 sec relaxation, quadriceps and rotators stretch held for 30 sec.
4-12	Quadriceps strenghtening	Sitting isokinetic contractions	To increase strength of knee extension and vastus medialis strengthening.	3x10
		Ball squats- with ball behind the back		3x10
		Step ups		3x8
		Step downs		3x8
		Single leg ¼ squat		3x8
		Foam roller extensions (no weight)		3x10
8-12	Functional training	Side to side lunge	To strengthen femoral and hip muscles as well to gain stability	3x8
		Lateral duck under squats		3x8
		½ squat, ½ deadlift		3x8
		Step up/downs		3x5
		Rotational step up		3x5
	CORE exercises	Bridge	Strengthens hip abductors	3x10
		Clamshell exercises with Resistance Band		3x10
	Bad movement patterns	One leg deadlift	Correct bad movement during exercises	3x8
		Supported squat		3x10
		Bear squat (bear exercise position and squatting backward)		3x10

Therefore, the previous conservative interventions were followed with viscosupplementation injections performed by the physician (SynVisc, HyalganGF-20) on both knees (injections in each knee joint once a week for three weeks) in order to reduce friction, and the use of NSAID drugs to relieve pain.

Subsequently, extracorporeal shock wave therapy (ESWT Rosetta System, CR Technology) was initiated on both knees during further strengthening exercises.^10,11 Shock wave therapy was applied directly to the source of pain in the region of the bipartite patellae. On MRI there was bone edema noted, which is related to an increase in interstinal fluid and believed to be a source of pain. ESWT is believed to act physically on the tissue by inducing an acute inflammatory reaction, as well as increasing blood flow and oxygen supply. It also is suggested to enhance tissue healing and has some analgesic effect. Recent evidence suggests that ESWT therapy shows significantly better clinical results in decreasing pain caused by bone marrow edema than drug interventions.¹¹ In this case report ESWT was used to reduce bone edema and the pain caused by it. The interval between shock wave treatments was five days. At first patient reported a mild pain increase to VAS 7/10 after ESWT procedure from the initial VAS pain scores of 5/10 in both knees. The ESWT therapy consisted of five sessions delivered using medium energy of 0.55mJ/mm² of about 1000 impulses each treatment session.^10,11 After three weeks of ESWT, the subject showed dramatic improvement, and the VAS decreased to 0/10 in the left knee and 1/10 in the right knee.

The Kujala Score in the left knee after treatment improved to 100 and in the right knee 95. After improvement patient was tested with single leg squat, leg crossover hop, vertical jump and four hop double leg jump with no pain and discomfort during exercises. (Table 3) Full painless range of motion was achieved in both knees. Patient returned to her sport activity with no pain during squats, cycling and jumping.

Table 3.

Functional tests final measures

Test	Final measures
	Left	Right
Single leg squat	5 rep (without pain and knee giving way)	5 rep (without pain and knee giving way)
Leg crossover hop	402 cm	398 cm
One leg Hoop	104 cm	102 cm
Vertical jump	51 cm
Triple hop, double leg jump	405cm	405cm

DISCUSSION

For most anterior knee pain syndromes, the exact cause of pain remains unknown. Therefore, most agree that conservative interventions should be the first choice of treatment. In cases of bipartite patellae the proposed source of pain is the gap between bony fragments. Oohashi et al¹² examined the interposed tissue harvested from the gap between the fragment and the body of the patella during surgery and found many histological tissue types: fibrous and fibrocartilage tissue, as well as hyaline cartilage. In the interposed tissue, pathological abnormalities were also observed like diffuse degeneration and necrosis, focal necrosis of the fibrocartilage and trabecular bone, and lack of blood vessels. The bone marrow adjacent to the interposed tissue, however, showed multiple blood vessels, and trabecular bone surfaces were filled with numerous osteoclasts.¹² This avascular tissue in the gap may prevent an accessory ossification center from allowing unification with the main portion of the patella. Additionally, the accessory fragment may be pulled aside by soft tissue structures similar to vastus medialis muscle or the retinacula, a mechanism which also inhibits bony union like in avulsion type fractures. Some authors report initial onset of clinical symptoms in those with bipartite patellae after trauma or overuse activities, which may be explained by “overstretching” of the fibrous gap.^3,13

The subject of this case report experienced chronic pain at the gap between patella fragments bilaterally. The rehabilitation plan was multifaceted, including stretching and flexibility exercises that would reduce tension on the additional fragment, quadriceps strengthening exercises to strengthen the knee extensors, including the vastus medialis. ESWT was added in order to provide a resolution of the inflammatory condition that could be contributory to the pain at the gap between the patellar fragments.

Sustained traction acting on the patella laterally and proximally is presumed to cause the pain in the anterior part of the knee, since other abnormalities are rarely seen. In a MRI study of 53 patients with bipartite patella, bone marrow edema within the accessory fragment was the sole finding on knee MRI in the majority of the patients.⁴ In a histological study the articular cartilage was intact in most of the patients.¹² Most of the cases of painful bipartite patella have been treated using conservative physical therapy treatment including rest, stretching exercises, strengthening exercises, and bracing, and responded to them well.^14,15 Although early conservative treatment was not effective for this subject (in a different organization), the combination of physical therapy, other modalities, and medical management proved to be effective for this subject with long lasting pain and limited function caused by bipartite patella. ESWT may have a neo-angiogenetic, anti-inflammatory and pain decreasing effect which worked well in this condition alongside with rehabilitation program.^10,11

LIMITATIONS

There were several limitations regarding this case report. The findings from a case report cannot be generalized to all subject populations. High quality randomized control trials are needed to document ESWT in treatment of bipartite patella pain. The subject was treated with conservative treatment before the described procedures, which could also have had some effect on the presentation or resolution of knee pain over time. At the beginning of treatment no objective measures of strength were taken, which would enhance the ability to determine changes in strength over time. However, the described therapy allowed the subject recovery to pain free status and return to preferred sport activities.

CONCLUSIONS

Even though only three typical types of bipartite patellae have been previously described, clinicians should be aware of the possibility of medial bipartite patella in cases of medial peripatellar knee pain. The medial bipartite patella is a rare finding but can be treated successfully as demonstrated in this case by a non-operative physical therapy approach including stretching and flexibility exercises, quadriceps strengthening, and ESWT.